Chemistry of Polycyclic Aromatic Hydrocarbons Formation from Phenyl Radical Pyrolysis and Reaction of Phenyl and Acetylene

Abstract

An experimental investigation of phenyl radical pyrolysis and the phenyl radical + acetylene reaction has been performed to clarify the role of different reaction mechanisms involved in the formation and growth of polycyclic aromatic hydrocarbons (PAHs) serving as precursors for soot formation. Experiments were conducted using GC/GC-MS diagnostics coupled to the high-pressure single-pulse shock tube present at the University of Illinois at Chicago. For the first time, comprehensive speciation of the major stable products, including small hydrocarbons and large PAH intermediates, was obtained over a wide range of pressures (25-60 atm) and temperatures (900-1800 K) which encompass the typical conditions in modern combustion devices. The experimental results were used to validate a comprehensive chemical kinetic model which provides relevant information on the chemistry associated with the formation of PAH compounds. In particular, the modeling results indicate that the o-benzyne chemistry is a key factor in the formation of multi-ring intermediates in phenyl radical pyrolysis. On the other hand, the PAHs from the phenyl + acetylene reaction are formed mainly through recombination between single-ring aromatics and through the hydrogen abstraction/acetylene addition mechanism. Polymerization is the common dominant process at high temperature conditions.

Structure of incipiently sooting ethylene–nitrogen counterflow diffusion flames at high pressures

“…Shock-tube [10][11][12] and plug flow reactors [13] are one-dimensional, and are typically used for high-pressure modeling. However, they do not present the coupling between kinetics and transport of flames, with potential consequences on the sequence and the relative importance of reactions that occur in flames.…”

Theoretical study of the triplet state aryl cations recombination: A possible route to unusually stable doubly charged biphenyl cations

“…The reactions of phenyl radicals are gaining interest among the study of the carbonaceous soot particles formation mechanism and their precursors, such as polycyclic aromatic hydrocarbons due to their importance in combustion, atmospheric, interstellar, and graphene chemistry . The diazonium salt‐derived phenyl (aryl) radicals known as effective grafting agents for metal and organic surfaces provide an additional reason for the extensive study of these species .…”

An Accurate Molecular Structure of Phenyl, the Simplest Aryl Radical

“…In combustion, for example, these models make predictions about fuel efficiency and can be used to minimize negative environmental and health impacts arising from polycyclic aromatic hydrocarbon and soot formation. [7] Because reactivity is closely linked to the various properties of the unpaired electron, it is important that theoretical methods describe the radical site accurately. Owing to effects such as electron correlation and spin contamination, s-type aromatic radicals pose one of the more difficult challenges for quantum chemistry.…”

“…Essentially the full gamut of theoretical approaches has been employed to predict the structure and properties of C 6 H 5 C, including Hartree-Fock, Møller-Plesset perturbation theory (MP2), CASSCF, coupled cluster, and density functional methods. [4,7,8] The phenyl radical has a planar geometry, a 2 A 1 ground electronic state, and C 2v symmetry. It has been extensively studied in the condensed phase; [9] in the gas phase, its Figure 1.…”